The present invention relates to an injection molding apparatus and process for forming an assembled article from two complementary molded parts and, more particularly, to an unloading and assembly system for use in said injection molding apparatus.
Multi-piece articles and the components therefore are often injection molded in stack mold machines. Articles so produced include floppy disk shells, DAD boxes and Petri dishes having a molded base and a molded cover. Stack molds are used because numerous components can be formed in a single cycle. A family stack mold having eight cavities per half is typically used to manufacture Petri dish components. In such a molding system, eight bases and eight covers are molded in a single cycle.
After components are molded, they are removed from a stack mold machine in a number of ways. For example, the components may be removed using a guide rail system such as that shown in U.S. Pat. No. 3,910,740 to Rees. The removed components are then conveyed to an assembly machine such as that shown in U.S. Pat. No. 3,938,675 to Rees for mating one component to another. The assembly machine, in addition to automatically assembling the articles from its components, presents a counted stack of articles for packaging. Where the components being formed are Petri dish components, the conveyor systems are closed so as to reduce potential contamination.
In an alternative removal system, the parts are removed using a robot. The deficiency with this approach is that cycle time is penalized. This occurs because the robot requires a finite amount of mold open or wait time to remove the parts.
In still another system, sterilized air is used to blow molded parts down a vertical guide conduit. U.S. Pat. No. 4,422,998 to Sorenson illustrates this type of system.
Cycle times associated with stack mold machines have been improved through the use of a pivoting part removal device that deposits molded parts in a vertical chute mounted alongside the mold. Pending U.S. patent application Ser. No. 353,243, filed May 17, 1989, to DiSimone illustrates a stack mold system having such a part removal device.
Improvements in cycle time have created other problems however. For example, systems having a shorter cycle times create more components for assembly. As a result, the speed of the associated assembly machine(s) must be increased to keep up with the rate of molding. A typical molding rate is eight sets of article components every six seconds or approximately 80 per minute. At such rates, assembly machines are prone to jamming and somewhat unreliable.
The foregoing problems are complicated during the manufacture of Petri dish components by the need to maintain as much of a sterile environment as possible. Handling methods such as guide rails and robots allow the interior surfaces of both the base and cover components to be exposed to the atmosphere for sufficient periods of time to reduce their sterility. As a result, the components must be sterilized after assembly. This is typically done by subjecting the assembled and packed Petri dishes to gamma radiation or by placing the packaged and assembled Petri dishes in a container which is flooded with ethylene oxide gas for several hours. The cost associated with such sterilization procedures is on the order of $6.50 per 500 assemblies. This cost represents a significant portion of the product's overall cost. Typical costs for the resin material used to produce the Petri dish components is about $8.50 per 500 assemblies.
Improvements in overall production could be obtained if these problems could be eliminated or overcome.
Accordingly, it is an object of the present invention to provide a process and apparatus for forming injection molded components and for assembling these components into a desired article immediately after demolding.
It is a further object of the present invention to provide a process and apparatus as above which eliminates the need for separate assembling machines and sterilization equipment.
It is yet a further object of the present invention to provide a process and apparatus as above which decreases the cost for producing injection molded article.
These and further objects and advantages of the present invention will become clearer from the following description and drawings in which like reference numerals depict like elements.